Smooth Muscle Tissue - Downing Flashcards
Where do you find smooth muscle in the body?
Walls of hollow viscera (GI; Reproductive; Urinary; Respiratory)
Walls of blood vessels
Larger ducts of some compound glands
Small bundles in skin (arrector pili muscles)
nipple and scrotum
What is the shape of smooth muscle?
fusiform (tapered ends)
What regulatory components are present or absent in smooth muscle?
Tropomyosin present (maybe not so important tho)
Troponin absent
How are actin and myosin organized in the smooth msucle?
Actin and myosin filaments are not arranged in the precise manner noted in skeletal and cardiac muscle. They tend to form bundles that run obliquely through the cytoplasm
What role do dense bodies play in smooth muscle?
Two locations
- Inner aspects of sarcolemma
- Randomely throughout cytoplasm
Comparable to Z-disks of skeletal & cardiac muscle
Contain alpha-actini
Serve as anchor sites for actin-myosin interactions as well as intermediate filaments (vimentin; desmin)
What are caveolae? What is their role in smooth muscle?
Pinocytotic-like invaginations of sarcolemma
Probably play the role of the T-tubules found in skeletal and cardiac muscle
May work in concert with sarcoplasmic reticulum to modulate Ca++ availability
What is the mechanism of contraction in smooth muscle?
- Ca/Calmodulin form a complex
- Complex activated myosin light chain kinase
- kinase phosphorylates one of the two light chains associated with myosin head
- This phosphorylation exposes the actin binding site on the myosin molecule
- myosin can then straighten out to form small bipolar filaments
What is the rate difference between smooth muscle vs skeletal/cardiac?
Smooth muscle contraction takes longer and is more prolonged than skeletal or cardiac muscle contraction
REVIEW QUESTION:
What kind of neurotransmitter is found in the synapses innervating sympathetic and parasympathetic connections to the muscle?
Sympathetic: synaptic vesicles contain norepinephrine
Parasympathetic: synaptic vesicles contain acetylcholine
If only a small percentage of smooth muscle cells are actually innervated, then how are the other muscle cells stimulated to contract?
Impulse transmission from muscle cell to muscle cell accomplished via gap junctions
(In the iris of the eye, EVERY muscle fiber is innervated)
What does it mean for muscle to regenerative and what is an example of this in the body?
It means that cells retian their mitotic capability
An example is the pregnant uterus
What are the general characteristics of smooth muscle?
- No striations
- No t-tubules
- Involuntary
